Perspectives and opportunities for intensity interferometers

Abstract

Stellar intensity interferometry (SII) promises significant gains in angular resolution that is well beyond what is currently available. Hanbury Brown in the 1960s measured the diameters of 32 stars, mainly on the main sequence, at his Narrabri SII setup at resolutions of 500μas, heralding the age of quantum optics [1]. To realise the potential of SII further, arrays of 10s, 100s or even 1000s of rudimentary telescopes sampling baselines up to many kms are required. The number of telescopes and their separations determine the quality of the derived images. Recently SII has undergone a renaissance thanks to advances in detector technology, limitations in amplitude interferometry and demonstrations in the laboratory of photon time-tagging and off-line correlation. Data from existing Cherenkov telescope arrays: VERITAS, HESS and MAGIC are breaking new ground. ASTRI, a 9-telescope array on Tenerife, will access 36 static baselines, increasing to ~400 as the target traverses the sky. Furthermore the implementation of SII options on the CTAO arrays both in Chile and on La Palma would represent a significant advance. However it is becoming clear that a purpose-built intensity interferometer array would enable SII to come of age, delivering unprecedented scientific opportunities and obviating the need to be a lesser scientific programme on facilities built for other purposes. Such an array would be SIITAR, the Stellar Intensity Telescope ARray, an extensive stand-alone observatory dedicated to imaging stars, their dynamics and their interactions. Its angular resolution would be ~5μas.